# Longest Common Prefix Matching | Set-6

Given a set of strings, find the longest common prefix.

Examples:

```Input: str[] = {geeksforgeeks, geeks, geek, geezer}
Output: gee

Input: str[] = {apple, ape, april}
Output: ap```

Previous Approaches: Set1 | Set2 | Set3 | Set4 | Set5

Approach:

• Sort the given set of N strings.
• Compare the first and last string in the sorted array of strings.
• The string with prefix characters matching in the first and last string will be the answer.

Below is the implementation of the above approach:

## C++

 `// A C++ Program to find the longest common prefix` `#include ` `using` `namespace` `std;`   `// A Utility Function to find the common prefix between` `// first and last strings` `string commonPrefixUtil(string str1, string str2)` `{` `    ``string result;` `    ``int` `n1 = str1.length(), n2 = str2.length();`   `    ``// Compare str1 and str2` `    ``for` `(``int` `i = 0, j = 0; i <= n1 - 1 && j <= n2 - 1; i++, j++) {` `        ``if` `(str1[i] != str2[j])` `            ``break``;` `        ``result.push_back(str1[i]);` `    ``}`   `    ``return` `(result);` `}`   `// A Function that returns the longest common prefix` `// from the array of strings` `void` `commonPrefix(string arr[], ``int` `n)` `{` `    ``// sorts the N set of strings` `    ``sort(arr, arr + n);`   `    ``// prints the common prefix of the first and the` `    ``// last string of the set of strings` `    ``cout << commonPrefixUtil(arr[0], arr[n - 1]);` `}`   `// Driver Code` `int` `main()` `{` `    ``string arr[] = { ``"geeksforgeeks"``, ``"geeks"``,` `                     ``"geek"``, ``"geezer"` `};` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]);`   `    ``commonPrefix(arr, n);`   `    ``return` `0;` `}`

## Java

 `// A Java program to find the longest common prefix `   `import` `java.util.Arrays;`   `class` `GFG {`   `// A Utility Function to find the common prefix between ` `// first and last strings ` `    ``static` `String commonPrefixUtil(String str1, String str2) {` `        ``String result = ``""``;` `        ``int` `n1 = str1.length(), n2 = str2.length();`   `        ``// Compare str1 and str2 ` `        ``for` `(``int` `i = ``0``, j = ``0``; i <= n1 - ``1` `&& j <= n2 - ``1``; i++, j++) {` `            ``if` `(str1.charAt(i) != str2.charAt(j)) {` `                ``break``;` `            ``}` `            ``result += str1.charAt(i);` `        ``}`   `        ``return` `(result);` `    ``}`   `// A Function that returns the longest common prefix ` `// from the array of strings ` `    ``static` `void` `commonPrefix(String arr[], ``int` `n) {` `        ``// sorts the N set of strings ` `        ``Arrays.sort(arr);`   `        ``// prints the common prefix of the first and the ` `        ``// last String of the set of strings ` `        ``System.out.println(commonPrefixUtil(arr[``0``], arr[n - ``1``]));` `    ``}`   `// Driver Code ` `    ``public` `static` `void` `main(String[] args) {` `        ``String arr[] = {``"geeksforgeeks"``, ``"geeks"``,` `            ``"geek"``, ``"geezer"``};` `        ``int` `n = arr.length;`   `        ``commonPrefix(arr, n);`   `    ``}` `}` `/* This JAVA code is contributed by 29AjayKumar*/`

## Python3

 `# A Python 3 Program to find the ` `# longest common prefix`   `# A Utility Function to find the common ` `# prefix between first and last strings` `def` `commonPrefixUtil(str1, str2):` `    ``n1 ``=` `len``(str1)` `    ``n2 ``=` `len``(str2)` `    `  `    ``result ``=` `""` `    `  `    ``# Compare str1 and str2` `    ``j ``=` `0` `    ``i ``=` `0` `    ``while``(i <``=` `n1 ``-` `1` `and` `j <``=` `n2 ``-` `1``):` `        ``if` `(str1[i] !``=` `str2[j]):` `            ``break` `        ``result ``+``=` `(str1[i])` `        `  `        ``i ``+``=` `1` `        ``j ``+``=` `1`   `    ``return` `(result)`   `# A Function that returns the longest ` `# common prefix from the array of strings` `def` `commonPrefix(arr, n):` `    `  `    ``# sorts the N set of strings` `    ``arr.sort(reverse ``=` `False``)`   `    ``# prints the common prefix of the first ` `    ``# and the last string of the set of strings` `    ``print``(commonPrefixUtil(arr[``0``], arr[n ``-` `1``]))`   `# Driver Code` `if` `__name__ ``=``=` `'__main__'``:` `    ``arr ``=` `[``"geeksforgeeks"``, ``"geeks"``,` `                    ``"geek"``, ``"geezer"``]` `    ``n ``=` `len``(arr)`   `    ``commonPrefix(arr, n)` `    `  `# This code is contributed by` `# Sanjit_Prasad`

## C#

 `// C# Program to find the longest ` `// common prefix ` `using` `System;`   `class` `GFG` `{` `// A Utility Function to find the common ` `// prefix between first and last strings ` `static` `String commonPrefixUtil(String str1, ` `                               ``String str2) ` `{` `    ``string` `result = ``""``; ` `    ``int` `n1 = str1.Length, n2 = str2.Length; ` `    `  `    ``// Compare str1 and str2 ` `    ``for` `(``int` `i = 0, j = 0; ` `             ``i <= n1 - 1 && j <= n2 - 1; i++, j++) ` `    ``{ ` `        ``if` `(str1[i] != str2[j]) ` `            ``break``; ` `        ``result += (str1[i]); ` `    ``} ` `    `  `    ``return` `(result);` `}`   `// A Function that returns the longest ` `// common prefix from the array of strings ` `static` `void` `commonPrefix(String []arr, ``int` `n)` `{` `    ``// sorts the N set of strings ` `    ``Array.Sort(arr);`   `    ``// prints the common prefix of the first ` `    ``// and the last String of the set of strings ` `    ``Console.Write(commonPrefixUtil(arr[0], ` `                                   ``arr[n - 1]));` `}`   `// Driver Code ` `public` `static` `void` `Main() ` `{` `    ``String []arr = {``"geeksforgeeks"``, ``"geeks"``,` `                    ``"geek"``, ``"geezer"``};` `    ``int` `n = arr.Length;` `    ``commonPrefix(arr, n);` `}` `}`   `// This code is contributed by 29AjayKumar`

## PHP

 ``

## Javascript

 ``

Output

`gee`

Time Complexity: O(N * log N)

The space complexity of the given program is O(M), where M is the length of the longest string in the array. This is because the program only requires additional space to store the result string, which can be at most M characters long. The rest of the program does not use any significant amount of extra space.

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